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cowl flaps

R

RV8R999

Well Known Member
I've tweaked my cooling system to provide just what I want for High DA, High GW, Vy climb to altitude by sealing every possible gap in baffles, between cyl, and inlets, I've added louvers to the lower exit area for increased mass flow, have the Oil cooler blocked 60% and can consistently climb at Vy to any altitude without any cyl exceeding 400 deg and most of the time never above 390. At Vmax (2700rpm limited FP) of 191 MTAS (68% power) 8K DA, CHTs range from 296 - 308. The low cruise CHTs provide plenty of margin to start throttling the exit for decreased cooling drag while leaving the modifications in place for climb. The only way to do this is to have an inflight variable exit area or cowl flap. My max exit area is fixed and set for the climb conditions discussed. My cowl flaps primary purpose is to allow a reduction in exit area while closed with perhaps some marginal benefit while open in reducing the pressure at the exit to further aid in climb cooling.
29wlvys.jpg

k3liqf.jpg


in the closed position very little increase in frontal area exposed to freestream while taking advantage of the sloping exit ramp to decrease the area. ratio of exit areas from open/ closed is approx. 1/.65 - remember when open the exit area remains 1/1 with the mods I've already made.

o9hn5z.jpg


In the down position no net change in exit area but may have some benefit of pressure reduction to help the flow - not counting on this and don't really care as the system is set-up for this exit area already.

nlr29s.jpg


Probably need a bit more clearance with the exhaust. I will probably cut an inch or so off the exhaust pipe.

210d25w.jpg


The cowl flap is not hinged to the cowling yet it is just resting in place.

Now the hard part: how do I actuate the flaps? I have some ideas but would be interested in the collective brain trust.

Whatever the method it has to be able to hold the flap both open or closed (and in between) AND be easy to disconnect for cowl removal.

What say you?
 
An electric servo actuator, controlled with a closed-loop controller on max CHT measurement, perhaps...? :D
 
Firgelli Linear Actuator

We have a cowl flap on our (Wilksch Diesel) RV. We use a Firgelli Linear Actuator firgelli.com

We use an L-16S with the 150:1 gearing and it is fine so far. The built-in limit switches make it simple to install and we figure we have little need for fine control of the flap position. We control it with an on-off-on DPDT switch and wangled the actuator geometry to get the range of movement we required. It was way simpler to install than the push-pull cables we tried previously.
 
Whatever the method it has to be able to hold the flap both open or closed (and in between) AND be easy to disconnect for cowl removal.
Click to expand...

Hinge the assembly from the airframe, rather than the cowl, and you won't need to disconnect anything for cowl removal.
 
ken

I have built a similar exit fairing (non movable) for my -6.

My cooling was already very good but I found that the airflow at the corner where the cowling meets the firewall has very poor flow and I was looking to straighten flow in that area to reduce drag (increase speed). I realize that the 8 is different than the 6, but I think that the same issues exist to some extent.

I got much improved flow in this area as evidenced by very streamlined oil traces aft of the cowl outlet. I got about 4 knots and 15 - 20 degrees reduction in CHT at cruise.

As an alternative to cutting the exhaust, consider cutting back the fairing just around the exhaust pipe to obtain clearance. That is how mine is and I have no problem with the fairing within about 3/4" of the pipe and the fairing insulated with some aluminum tape (available at auto parts stores).

I also second Dan's suggestion about mounting the fairing to the fuse. That's how mine is and it does not complicate cowl removal as it would if mounted to the cowl.

Send me a PM with your e-mail address and I'll send you a quick sketch of one possible actuation scheme that might work. Good luck with the mod.
 
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Thanks for the ideas!

Some great ideas.

The idea of closed loop control is interesting but for sure would need to feebback both CHT (highest) AND flap position otherwise it would end up being a bang-bang type-1 system and probably exceed the duty cycle of most linear actuators. I'm sure there are several actuators with position feedback available I just haven't researched it..

DanH said:
Hinge the assembly from the airframe, rather than the cowl, and you won't need to disconnect anything for cowl removal.
Click to expand...

I like this idea but to keep the axis of rotation co-located with lower cowl exit edge I'll have to fab some brackets which extend from the lower firewall face to the hinge line.

For now I went with extra flap hinge attached to the cowl exit edge and riveted support brackets and a lever arm. Ultimately I like the idea of a linear actuator but until I am convinced this is going to work I routed an extra cable I had and connected to the lever arm with a set screw. It took me 2 minutes to connect once I had it all trimmed and set up correctly. If it becomes a pain to remove I'll switch to fuse mounted hinges.

I decided pulling the knob back to open was most intuitive to me and since the cable is very flexible it made more sense to it in tension when the flaps are deployed.

I located the pull knob on the left side high on the gear tower such that when I am WOT I can reach the knob with two fingers while still maintaining hand on throttle.

2qcgxi0.jpg


x0ratc.jpg

2j2xrhy.jpg


Full down. I adjusted for a bit of an extreme angle but probably will not operate like this other than for testing.
2lnnti.jpg


Ran at 1000RPM (on the ground) with EGTs 1100 for about 20 minute in both open and closed position. One interesting result was a discernible muffling effect when closed.

No burning of the glass noted but I'm not convinced the assembly is stiff enough. I'm going to add more layers of glass before I fly as the actuating lever is attached to the right side only resulting in too much flexibility when pushing from the aft left corner plus minor sinus congestion has me grounded anyway... Oh and a typical Florida afternoon thunder storm
 
Cowl flaps, automatic cowl flap actuator.

Hi Ken:

In Tony Bingelis book Firewall Forward on page 140 he describes a "automatic cowl flap actuator" that may be exactly what you are looking for. Porsche or VW cooling air intake bellows are used to automatically open or close the cowl flap.

The bellows expansion range is from 1 1/8" at 70 degrees F. to 4" at 250 degrees F.

The bellows look to be very compact and Tony has sketches showing how he installed it in a Globe Swift.

If you don't have access to the book, I'd be glad to scan it and email it to you. Or perhaps post it somewhere.



cheers, Terry.
 
book

Thanks Terry - I have the book somewhere here in my den. Don't remember ready about the bellows. I'll check it out. Thanks!

Ken
 
Cowl flaps, automatic cowl flap actuator.

Hi Ken:

If you study the second drawing, it shows a manual override plus a position indicator.


Keep us posted, I'd like to do something like this on my RV-6A.



Terry.
 
Flight Test

added several layers to stiffen the cowl flap and re-installed. Flew the same Vy climb profile I flew last week to 6000 ft PA WOT but with Cowl Flap full open. I did have to hold onto the knob during the first 2000ft as it wanted to close to about half open. Here is the data compared to the flight without cowl flaps. OATs were within 1 deg from t/o to 6K and I started both with #2 at 350 (this is a plot of just #2)
b3ws42.png



The slope of the linear section of decreasing temperature is more than twice that of decreasing OAT as a function of altitude.

Then with flap fully closed I accelerated to Vmax and stabilized. Because I have a FP prop I cannot really use Vmax as a criteria for decreased drag because I'll reach the 2700 RPM limit at TAS of 191 and end up throttling back to 2700rpm. The better measure is %power and FF at 191 MTAS. Without cowl flaps at 10000ft DA it required 64% power at a FF of 15.2 gph to achieve 191MTAS in steady level flight. Today with cowl flaps closed I reached 191MTAS at 10000ft DA with 62.5% at FF of 14.8. CHTs without flaps were 291,313,316,304 with flaps installed and closed : 282, 317, 306, 287 OT were unaffected by installation and operation of cowl flaps.

I'll need to run several more power comparisons at various DA's to verify results as FF in particular isn't the steadiest of data...but based on this I think I can throttle the exit further...

It sounds like a Harley now :)
 
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As you proceed along this line of testing you will, based on my experience, not see much benefit until you start to seal the lower plenum. The lower plenum air will look for other places to escape the cowling and the associated drag will negate your efforts. There are four areas that you can work on.
1. Remove the louvers, or at least tape them over for testing
2. Seal around the prop flange so air can not escape between your spinner and cowling
3. Seal around the upper gear leg farings so that no lower plenum air can get into the upper farings and gear legs
4. Internal ducting of air in the lower cowling towards the exit area
 
MauiLvrs said:
Seems like a lot of work for ~3 deg ....
Click to expand...

It wasn't "work" per se as I enjoy it. Plus it isn't just about the peak temperature either...look at the time the CHT is above 390 without flaps and with. Plus the goal wasn't to lower the CHTs during the climb anyway as I am happy with how the system performs without flaps. Nobody really knows the long term affect of climb with peak CHTs at 400 vs 390 vs 300 since the engine was designed for TBO with CHT between 300-400 optimal per the manual, if 400 is too high then the limit would be 390 and so on:

"Never exceed the maximum redline cylinder head temperature limit of 500 deg F. For maximum service life, CHTs should be maintained below 430 deg F during high performance cruise operation and below 400 deg F for economy cruise operation, with 300-400 optimal."

Even without flaps CHTs were at or near 400 deg F for about 2min. If we make an assumption a sortie length is 1 hr then during each sortie the engine is at the peak of "optimal" for 1/30th of each sortie or 66.6 hrs of its 2000 hour TBO. Even less during normal cruise climbs at 130 MPH vice 110mph. Who knows how many engines operate continuously at above optimal and go to TBO but 66 hours out of 2000 is fine by me. (admittedly a very simplified analysis)

Since both curves begin to drop shortly after peak at more than twice the adiabatic lapse rate (rate of OAT decrease with altitude) the system has excess cooling capacity at Vy. The reason CHTs rise so quickly is due to the imbalance of heat vs cooling during take-off. Because of this it will always be difficult to compare results between aircraft of different configurations. A plane with a C/S prop can probably accelerate to Vy faster than my FP prop and therefore begin the cooling process sooner preventing CHTs from peaking as high (my theory anyway). If this is true then Gross Weight will have an affect on cooling curves. Ever notice climb CHTs higher with a passenger - I have. I'd say the perfect system would keep all CHTs at 400 during the climb closing the exit as OAT decreases with altitude.

During todays test I am going to fly the same profile except I'll start from a low pass over the runway at Vy and record the CHTs in the climb. Not sure I'll be able to get #2 CHT to 350 at the start of this test but I'll make a standard T/O test with #2 below 300 so I can compare the two results.

Tom Martin said:
As you proceed along this line of testing you will, based on my experience, not see much benefit until you start to seal the lower plenum. The lower plenum air will look for other places to escape the cowling and the associated drag will negate your efforts. There are four areas that you can work on.
1. Remove the louvers, or at least tape them over for testing
2. Seal around the prop flange so air can not escape between your spinner and cowling
3. Seal around the upper gear leg farings so that no lower plenum air can get into the upper farings and gear legs
4. Internal ducting of air in the lower cowling towards the exit area
Click to expand...

1. Yes, covering the louvers this AM.
2. I'll put some thought into this..I've seen some interesting ideas but I'm not a fan of the spinner in contact with anything.
3. RV8 gear is not inside the cowl
4. Agree! Unfortunately with vertical induction an awful lot of "stuff" occupies the space near the exit. Would have been easier to build it into the system from the beginning as Dan did..but this is on the list.

Thanks for the inputs!

Ken
 
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RV8R999 said:
Since both curves begin to drop shortly after peak at more than twice the adiabatic lapse rate (rate of OAT decrease with altitude) the system has excess cooling capacity at Vy.
Click to expand...

Probably true. Minor notes....power is dropping with increasing alitiude, and cooling requirement is proportional to power output, yes? Also the lapse rate probably isn't consistent day to day.

2. I'll put some thought into this..I've seen some interesting ideas but I'm not a fan of the spinner in contact with anything.
Click to expand...

FWIW, Tom and I don't have seal contact with our spinners.
 
DanH said:
Probably true. Minor notes....power is dropping with increasing alitiude, and cooling requirement is proportional to power output, yes? Also the lapse rate probably isn't consistent day to day.



FWIW, Tom and I don't have seal contact with our spinners.
Click to expand...

Yes, good point. Actually for the past several weeks lapse rate has been very consistent here in Southern Florida +- 1 deg/1000ft PA variation
Contact with starter ring? Or just very close?

Flew same profile this AM but with Cowl Flaps fully closed. I did not cover the louvers yet. Again, environmental conditions within a deg to altitude. I am surprised by these results. The exit area (not counting all the leaks) is 2/3 of the original area when flaps are closed.
jzjiwn.png


Even more interesting is a comparison of the deltas from T/O to Peak CHT for each Cylinder with flaps open and closed. I'll need to run these tests a few more times at different Airspeeds.
16auueq.png
 
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RV8R999 said:
Contact with starter ring? Or just very close?
Click to expand...

Both I suppose. In my case the rubber baffle material has worn to a feather edge and the paint on the ring gear casting is polished smooth. Think of it as a "worn to fit" assembly. Tom uses bulk foam rubber in close compliance with a prop shaft extension. Very much doubt either is a true, airtight seal.

I am surprised by these results. The exit area (not counting all the leaks) is 2/3 of the original area when flaps are closed.
Click to expand...

....yet CHTs are lower than no flap at all?

Two possibilities. You may have more of a cowl exit extension than an area reduction, and the new, more aft exit point is an area of lower pressure. Or the exhaust is augmenting exit flow (my bet). Either would increase mass flow.

Wish you were recording manometer and air temperature measurements rather than just CHT.
 
DanH said:
Both I suppose. In my case the rubber baffle material has worn to a feather edge and the paint on the ring gear casting is polished smooth. Think of it as a "worn to fit" assembly. Tom uses bulk foam rubber in close compliance with a prop shaft extension. Very much doubt either is a true, airtight seal.



....yet CHTs are lower than no flap at all?

Two possibilities. You may have more of a cowl exit extension than an area reduction, and the new, more aft exit point is an area of lower pressure. Or the exhaust is augmenting exit flow (my bet). Either would increase mass flow.

Wish you were recording manometer and air temperature measurements rather than just CHT.
Click to expand...

I believe a bit of both. I choose the length of the flap to prevent a "knee" at the stock exit lip as the flap closes the exit area by taking advantage of the sloping ramp. The exhaust pipe exit is forward of the rear flap edge by 10" and within .75" of the flap itself, I have the same 4-to-1 exhaust you are using - augmentation is a real possibility here.

With louvers my inlet/exit ratios are:

Flaps open: 1/1
Flaps closed: 1/.79

Without louvers:

Flaps open 1/.86
Flaps closed 1/.65

but with all kinds of leakages these numbers don't mean much.

I started a complete Temp/Pressure mapping system about 6 months ago and got side-tracked. I will do this eventually. It will be interesting to watch P's & T's change with flap position in real time.

How did you seal the cowl seems? I know I have a ton of leakage around the top cowling at the fuse joint (I started a thread on this previously). I added several layers of glass to reinforce the cowl but still get significant bowing between skybolt fastners. I was going to order some VANs baffle material and add around the entire perimeter of the firewall and cowl halves. I suppose for testing I could duct tape the whole thing and see what happens.
 
RV8R999 said:
With louvers my inlet/exit ratios are: Flaps open: 1/1 Flaps closed: 1/.79 Without louvers: Flaps open 1/.86 Flaps closed 1/.65
but with all kinds of leakages these numbers don't mean much.
Click to expand...

Yeah, and everybody knows ratios like that won't work ;)

How did you seal the cowl seems?
Click to expand...

The long side seams got a glass lap flange, nutplates, and #8 screws. They're near air tight.

I too added glass tape (4 to 6 plies!) along the firewall perimeter seams for added edge thickness/stiffness, and kept the 1/4-turn spacing around 4". I can still see some bowing between the fasteners, in particular when I fly with the smallest exit. They surely leak pressure, so......

I was going to order some VANs baffle material and add around the entire perimeter of the firewall and cowl halves.
Click to expand...

On my list too, although I was thinking of a softer strip, without fabric reinforcement.

I suppose for testing I could duct tape the whole thing and see what happens.
Click to expand...

Racers....what kind of tape do we want? Duct tape can be hard on paint.
 
DanH said:
Yeah, and everybody knows ratios like that won't work ;)
Click to expand...

My instrumentation or flying technique must be way off :)

DanH said:
The long side seams got a glass lap flange, nutplates, and #8 screws. They're near air tight.
Click to expand...

If I'm not mistaken you are using the VANS hinge method on your cowl halves correct? I used Skybolt all around and therefore have a flange already - albeit leaky.


DanH said:
Racers....what kind of tape do we want? Duct tape can be hard on paint.
Click to expand...

ooh good point!
 
RV8R999 said:
If I'm not mistaken you are using the VANS hinge method on your cowl halves correct?
Click to expand...

Formed-in-place glass flange with nutplates and screws:

http://www.vansairforce.com/community/showthread.php?p=276028&highlight=flange#post276028

Hmmm....just had a thought not previously considered. The clamp force of a Skybolt fastener in tension is less than or equal to the stiffness of their little internal spring.....so a Skybolt can't stop a panel from blowing outward just a little bit when subjected to internal pressure. Good reason to add those rubber flap seals.
 
Ken and Dan,

You're right, don't use duct tape, and definitely don't use gorilla tape! It'll pull paint, and heat seems to make each leave a lot of gunky residue.

In most areas I use 3M 471 in the 2" width. Wide, flexible, does curves well with a little patience, and comes off fairly clean, especially if you don't leave it on too long (and goo-gone gets the residue). Doesn't pull paint, unless you have a chip and pull it off too fast. Kinda pricey.

However, on the cowl seams, I've been using a 1" wide clear vinyl tape that Mark Frederick brought to Reno this year. I believe it is this tape, as found on amazon.com. I'll contact Mark and double check, and ask him to look at this thread too. This stuff is very reasonably priced ($5 for 36 yds).

For the 3M 471, here's a link to today's search that shows pages of options for 471, in 1/2', 3/4", 1.5" and 2" widths. Not cheap stuff, especially the 2", but different colors have widely varying prices ($22 to $37 for a 36 yard roll)red and blue seem cheapest), but if its for testing, color is not an issue! Amazon has the best prices I've found (if ya beat it, please lemme know!)

Watching this thread with great interest and learning, as always. I think I've worked up the courage to work cowl issues this winter (those flames in $1,000/gallon paint have intimidated me till now!). Exit area work via a Dan-like changeable shrinking exit, closing that gap at the prop flange, firewall cleanup and internal ducting, and a new induction air intake scoop like a Rocket scoop are items on the drawing board.

Great discussion and great work Ken. Thanks for blazing trails to all of you!

Cheers,
Bob
 
DanH said:
Formed-in-place glass flange with nutplates and screws:

http://www.vansairforce.com/community/showthread.php?p=276028&highlight=flange#post276028

Hmmm....just had a thought not previously considered. The clamp force of a Skybolt fastener in tension is less than or equal to the stiffness of their little internal spring.....so a Skybolt can't stop a panel from blowing outward just a little bit when subjected to internal pressure. Good reason to add those rubber flap seals.
Click to expand...

wow..very nice work and undoubtedly well sealed.

agree about skybolt clamp force. Also wondering how much leakage through the skybolt hardware itself...I'll go check (don't ask).

What are your thoughts on attaching rubbers to the firewall perimeter? I have not found any adhesives which provide any longevity although I have not tried proseal (next to adel clamps the second most evil inanimate object).
 
rvmills said:
Ken and Dan,

You're right, don't use duct tape, and definitely don't use gorilla tape! It'll pull paint, and heat seems to make each leave a lot of gunky residue.

In most areas I use 3M 471 in the 2" width. Wide, flexible, does curves well with a little patience, and comes off fairly clean, especially if you don't leave it on too long (and goo-gone gets the residue). Doesn't pull paint, unless you have a chip and pull it off too fast. Kinda pricey.

However, on the cowl seams, I've been using a 1" wide clear vinyl tape that Mark Frederick brought to Reno this year. I believe it is this tape, as found on amazon.com. I'll contact Mark and double check, and ask him to look at this thread too. This stuff is very reasonably priced ($5 for 36 yds).

For the 3M 471, here's a link to today's search that shows pages of options for 471, in 1/2', 3/4", 1.5" and 2" widths. Not cheap stuff, especially the 2", but different colors have widely varying prices ($22 to $37 for a 36 yard roll)red and blue seem cheapest), but if its for testing, color is not an issue! Amazon has the best prices I've found (if ya beat it, please lemme know!)

Watching this thread with great interest and learning, as always. I think I've worked up the courage to work cowl issues this winter (those flames in $1,000/gallon paint have intimidated me till now!). Exit area work via a Dan-like changeable shrinking exit, closing that gap at the prop flange, firewall cleanup and internal ducting, and a new induction air intake scoop like a Rocket scoop are items on the drawing board.

Great discussion and great work Ken. Thanks for blazing trails to all of you!

Cheers,
Bob
Click to expand...


Bob, Thanks for all the info good stuff!
 
RV8R999 said:
wow..very nice work and undoubtedly well sealed.
Click to expand...
Concur, very nice. My cowl is done with nutplates and screws as well. Seems fairly tight, and I don't get much bowing between fasteners. However, I have seen small areas of cowl seam tape that appeared to have had some air blow-by. Leads me to believe this sealing is a very valuable exercise. I like the idea of the baffle material seal...cogitating on that.


RV8R999 said:
agree about skybolt clamp force. Also wondering how much leakage through the skybolt hardware itself...I'll go check (don't ask).
Click to expand...

Wear safety glasses! :) I have this mad scientist with compressed air vision in my head! Perhaps you could take it out on a couple adel clamps and launch them with the skybolt innerds when you find their critical pressure! ;)


RV8R999 said:
What are your thoughts on attaching rubbers to the firewall perimeter?
Click to expand...

Now that would look really strange...oh never mind...mind outta the gutter! :p


RV8R999 said:
I have not found any adhesives which provide any longevity although I have not tried proseal (next to adel clamps the second most evil inanimate object).
Click to expand...

That is a definite concern...how to hold them in place when there is no air pressure pressing them up or out into the seam...more cogitating!

Cheers,
Bob
 
Ken, I suspect that the general improved efficiency that you saw even with the cowl flap closed is due to improved exit airflow. Again, flow at the corners of the stock cowl outlet is bad. Giving that turbulent corner flow a chance to straighten and combine with the free stream air improves the exit flow considerably.

See my cowl exit fairing. Simple but good for 4 Knots and 15 - 20 degrees cooler CHT's.

68108668@N04


http://www.flickr.com/photos/68108668@N04/

Bob, I would be happy to send you my prototype made of aluminum if you want to play with it. It should fit your six cowl. Us Navy guys must stick together, especially if it means running down Rockets!!
 
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gereed75 said:
Ken, I suspect that the general improved efficiency that you saw even with the cowl flap closed is due to improved exit airflow. Again, flow at the corners of the stock cowl is bad. Giving that turbulent corner flow a chance to straighten and combine with the free stream air improves the exit flow considerably.

See my cowl exit fairing. Simple but good for 4 Knots and 15 - 20 degrees cooler CHT's.

68108668@N04


68108668@N04


http://www.flickr.com/photos/68108668@N04/

Bob, I would be happy to send you my prototype made of aluminum if you want to play with it. It should fit your six cowl.
Click to expand...

Interesting...
 
I have some additional refinements in the works along the lines of Tom Martin's suggestions back on page 2 -

"4. Internal ducting of air in the lower cowling towards the exit area"

When that boy speaks, it comes from many hours of experience with many mods and his results show it.

I'll continue to post as I learn. Continued good luck.
 
Gary,

I'd love to experiment with your prototype...thanks for the offer. I'll pay shipping! The aft edge of my exit is actually cut at a raking angle forward (rather that straight down). Not sure if one of the previous owners cut it to allow better cooling (at the expense of drag). The motor and oil cool very well, but I can see reverse airflow evidence aft of the exit in the form of oil drips swirling and moving forward. Much to be gained here, I believe, and Tom Martin's first advice to mr in this area was to build an extension much like you did. Great first step before I get brave and cut out an area to make a removable section as Dan did.

As for the internal ducting, John Huft did this well, and it was documented on his website, which appears to be down now. I may have a copy of the pics on my computer at home, and will post them if I do. They were basically curved vertical walls on the lower cowl, looked like 2-3" high, and curving from wider just behind the aft cylinders, to narrow at the exit (matched the exit width). John also ran a duct from his oil cooler to the exit too.

Interesting discussion that Ken's cowl flap may be more of an extension than a cowl flap. That may match Tom's experience too. Tom, IIRC, you saw no speed gain from your movable cowl flap, but when you closed the cowl around the prop shaft, your temps dropped and you were able to run with the cowl flap closed (exit throttled). Is that correct?

Its such an interesting interrelated system of systems!

Cheers,
Bob
 
gorilla super glue

well I can tell you gorilla super glue will not work.

tested a coupon of alum and vans baffle material with a drop of this super glue.

after about 2 minutes I was unable to pull apart in tension although I could tell peel strength was much less - probably not an issue for this application as it only really needs to support it's own weight (x6g) However, heat soaked at 200 deg in the oven for an hour and it was easy to pull apart in tension.

I'll try proseal tomorrow.
 
Bob, PM me with your address and I will send the fairing. You will probably have to mod it a bit to integrate with your trimmed back cowl. This should not be a problem for you with your new found master fabrication skills aquired with the new tail build!!

It is the reverse airflow at the outlet corners that I had hoped to address with this fairing. There is still evidence of stagnating flow at the corners, but no reverse flow and it is smoothed out by the time it exits into the free airstream. Improvement is evidenced by lower CHT's and higher speed. I have some pictures that show how stream lined (laminar??) my flow is behind this exit duct if you are interested.

This is similar to Tom's treatment in this area, but on the Rocket with the ramp the required fairing is much smaller. I recall him saying that he was not able to gain any speed with a movable exit flap.

I would like to see John's internal diffuser arrangement if you have the pix. I have something similar in the works that I hope will increase flow efficiency while also reducing outlet area slightly, but I suspect it will be simpler than John's.

I also did some very simple clean up of the exhaust hangars that are right in the exit flow. I'll have to get a picture of that if your interested.

I am taking an incremental system improvement approach. So far, I have taken no steps backward. That's a good thing.

Send address and my prototype is yours.

Fly Navy!!
 
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skybolts are like holes

Skybolts leak like sieves. I dab'd a bit of RTV in each one and allowed it to dry. Didn't interfere with the lock fitting and are now air tight.

Ordered some baffle material from VANs and will seal the prop flange in similar fashion as Dan as well as all the cowl seams.

I had about 10" of scrap material and affixed it to the upper firewall perimeter centered at the top to determine if this will alleviate the bowing between skybolt fasteners. Should provide some insight into whether or not installing this material is worth it or not. I'll let you know - going flying - no thunder storms this afternoon!
 
Cowl Seal and Louvers Blocked

Used vinyl tape to seal my cowl and a temp alum plate to block the louvers and then flew a Vy climb profile as previously. However, I did not wait for #2 to warm up to 350 as I wanted to be sure blocking the louvers wasn't going to create an overheating issue. I think the results are interesting but not surprising. I did conduct a Pmax run but I didn't have time to add fuel to ensure an apples to apples comparison as I'm about 15 gallons lighter today - no cheating!

It was about 8 degrees warmer at T/0 and through about 3000ft when temps became similar to previous runs.

I'm not making any conclusions about the louvers or sealing until I can complete a run with #2 starting at 350 tomorrow AM but here are the charts for comparison:

2hmzfpt.png

2crrgxz.png
 
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Gary, PM on the way, and thanks...let me know about shipping cost please...that's on me! Looked to see if I had a PIT overnight this month, but no cigar. Looks like I need to do a little before and after tuft testing! Ya know, if its fairly straightforward, if you want to send pics and a quick how-to paragraph, I can give it a go. Happy to play with your prototype though! Very generous offer! Also, I looked for the electronic version of John's pics, but I must have just printed them off his site. They are up at the hangar, so I'll bring them home tomorrow and scan them. Might be degraded a bit (scan of a so-so print) but might convey the concept OK.

Ken, when you ran the 10" test strip under the cowl, did you see any difference in the bowing between those fasteners? And did you perhaps see more bowing on the adjacent fasteners (or anywhere else). Or did you tape the same areas as well? My guess is that the air will find a way, and you won't see the full effect until you have a relatively complete seal. It would be interesting to compare the effect of a complete set of inner seam seals (baffle material), a completely taped outer seamline, and a combo of both. Temps will tell some of the story, but that's where Dan's manometer testing shines too, I'll bet. I'm not that sophisticated yet..more work to do! :eek:

Fun discussion!

Cheers,
Bob
 
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How 'bout a -10?

gereed75 said:
Bob, I would be happy to send you my prototype made of aluminum if you want to play with it. It should fit your six cowl. Us Navy guys must stick together, especially if it means running down Rockets!!
Click to expand...

Say Gary, my wife is a retired Naval Commander...does that count,:) because I'd love one for my-10, if the cowl exit opening is the same width as a -6. Mine measures 19" wide at the belly. IIRC, that's wider than the -6.

Best,
 
rvmills said:
Ken, when you ran the 10" test strip under the cowl, did you see any difference in the bowing between those fasteners? And did you perhaps see more bowing on the adjacent fasteners (or anywhere else). Or did you tape the same areas as well? My guess is that the air will find a way, and you won't see the full effect until you have a relatively complete seal. It would be interesting to compare the effect of a complete set of inner seam seals (baffle material), a completely taped outer seamline, and a combo of both. Temps will tell some of the story, but that's where Dan's manometer testing shines too, I'll bet. I'm not that sophisticated yet..more work to do! :eek:

Fun discussion!

Cheers,
Bob
Click to expand...

Bob - honestly because I tapped over all the seams it was difficult to determine if the section I applied baffle material was as "bowed" as the others. I suspect you are correct in that until the entire perimeter is sealed little difference will result.

Unfortunately this is my last couple days as a "retiree" as I start working for a living again on Monday so things will S L O W down significantly (pun intended)..
 
Pierre

Don't have a -10 near by and have not really looked to see how well this might work on a -10, but if the cowl outlet is similar to a -6, the basic concept will work. It is all about eliminating that revese flow at the corner and eventually smoothing the exit flow into the free stream.

I'll take a look at the next -10 I see.

Ummmm... wife and Navy CDR - she must never be wrong!

Ken, Congrats on retirement from REGNAV and Good luck with the new JOB!
 
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Pierre, I'll also take some pics and share whatever info Gary shares with me on the extension. Teamwork!

Congrats on the retirement and the new job Ken! Way to go, and thanks shipmate! Matter of fact, today is my first day of Navy retirement, so I'm now in the club with ya (I hit 30 in the Navy Reserve in September, so yesterday was my last official day aboard...spent it working on airplanes...a good day!)

Looking forward to your further testing Ken...looks like you're seeing some good results along the way!

Cheers,
Bob

PS: Funny comment about Pierre's retired CDR wife, and never being wrong! :) Then again, are any of our wives ever wrong?!? :D
 
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rvmills said:
Pierre, I'll also take some pics and share whatever info Gary shares with me on the extension. Teamwork!

Congrats on the retirement and the new job Ken! Way to go, and thanks shipmate! Matter of fact, today is my first day of Navy retirement, so I'm now in the club with ya (I hit 30 in the Navy Reserve in September, so yesterday was my last official day aboard...spent it working on airplanes...a good day!)

Looking forward to your further testing Ken...looks like you're seeing some good results along the way!

Cheers,
Bob

PS: Funny comment about Pierre's retired CDR wife, and never being wrong! :) Then again, are any of our wives ever wrong?!? :D
Click to expand...


Thanks Bob and congrats to you as well! 27 years active duty but I was ready to move on..

Waiting for the baffle material to arrive and I'll seal the rest of the cowl as well as the prop shaft. It'll be interesting to note the affect with prop shaft sealed.
 
Ken,
You asked about sealing against the ring gear casting. Working on my annual today so I took a cell phone picture of the wear area. Just a polished strip, not even worn through the paint.

inhkde.jpg


Early install photo, no wear yet:

5yghvr.jpg


Good luck on your first day at the new job.
 
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Finally grabbed the pic of John Huft's lower cowl to show a bit of his exit air ducting control measures. Apologies for the poor quality...his RV-8 site is down, so this is a scan of a pic I printed quite a while ago for reference material.

JH%252520Low%252520Cowl%252520duct_VAF.jpg


Appears John also incorporated a bit of an extension aft past the FW. The vertical walls of his ducts (or baffles) for exit air are somewhat visible at the edge of the silver heat shield material. The flange at the upper right end of the right duct wall is where John connected the scat tube coming off his engine baffle mounted oil cooler...he ducted that air to the exit too!

Smart (and fast) guy, that John!

Cheers,
Bob
 
cowl sealing

added baffle to the firewall perimeter and cowl seams.

Turns out #8 plastic caps fit snug overtop Skybolt fasteners and do a pretty good job of reducing leakage. Still a bit of leakage occurs where the fastener interfaces with the flange but it takes a good bit of pressure to get any flow through them. I ordered 50 more caps from Spruce to plug the remaining fasteners. Ended up using proseal and a few well placed flush rivets to hold everything in place. Also sealed
2i255xu.jpg


2djdik6.jpg


also sealed the prop flange much in the way Dan did and ran the engine at 1000rpm for about 20 minutes and then removed the cowl to check for wear and ended up trimming the material back another 1/4" as it looked a bit too tight for me:

1r6dfm.jpg


obvious rub marks on the starter ring as well as on the baffle material.

Ran out of daylight before it all came together.
 
DanH said:
Ken,
You asked about sealing against the ring gear casting. Working on my annual today so I took a cell phone picture of the wear area. Just a polished strip, not even worn through the paint.

inhkde.jpg


Early install photo, no wear yet:

5yghvr.jpg


Good luck on your first day at the new job.
Click to expand...

Somehow missed this post. Looks like your baffle seals about the same spot mine is. I ended up trimming mine back after the first run as it looked like it was butting to tightly against the back of the ring gear rather than the sloping forward section. Hoping the pressure of the lower plenum will close any gaps and provide an adequate seal. As you said earlier probably not air tight but a lot better than nothing. Thanks for the well wishes - first week as a civilian was INTERESTING!
 
Ken,
Cut a standard 6" diameter stick-on sanding disk (180 grit gold 3M) into strips, stick them to the flywheel, and run at 1000 for about 5 minutes.....trims the seal to the exact length.
 
DanH said:
Ken,
Cut a standard 6" diameter stick-on sanding disk (180 grit gold 3M) into strips, stick them to the flywheel, and run at 1000 for about 5 minutes.....trims the seal to the exact length.
Click to expand...

holy cow that is smart! Thanks for the tip.
 
Test Flight with Cowl/Prop Flange Sealed

Todays test flight results duplicating the same profile: CHT 2 @ 350 at T/O, Vy climb to 6K PA, OAT within 3 deg of previous test. Cowl Flaps were closed, louvers open during this flight.

Biggest difference today was the cowl and prop flange were sealed with baffle material.

Did notice a significant reduction in the bowing between skybolt fasteners during the climb but did not have a change to check at Vh as I wanted to minimize the flight time to give me a chance to check the prop flange baffle prior to reaching max RPM.

6du7tu.png


No earth shattering changes as expected but temps were hotter for longer than in same configuration without the cowl and prop flange sealed which makes sense to me as the TOTAL exit area has now been reduced, further choking mass flow - hence slightly higher temps. The small delta only means to me the leakage areas are a small percentage of the total exit area (Leakage/(designed area + leakage area)) and slight deviations in A/S and OAT contribute as well.

Tomorrows test will be with FLAPs open during climb and a Vh run with flaps closed.

then repeat with louvers closed.

BTW I tested the VANs baffle material for flammability. It burns easily when exposed to open flame and continues to burn freely once ignited. I'm going to rig up a piece over my belt sander and let it rip to see if I can get it to ignite from the friction. I'm still a little cautious about this stuff making contact with rotating parts for long periods of time but since Dan has had his since day 1 it is promising.
 
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As you close off outlet area (remove louvers for example) lower cowl pressure should rise.

As pressure rises the front seal should be pressed against the flywheel with more force. Note I installed aluminum fingers to support the seal strip.

I had the same friction concerns and do not discount them. At 144 hours there is no sign of heating/charing/etc at the feather edge of the seal strip. Keep an eye on it.

As you say, temperatures as expected. What about speed?
 
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